The invention relates to an improvement in the blockade drive mechanism for a bread packaging machine as described in U.S. Pat. No. 3,451,192 (Irwin) issued June 24, 1969. The machine described in U.S. Pat. No. 3,451,192 is used in the baking industry for packaging loaves of bread in inflatable plastic bags.
As described more fully hereafter, the blockade drive mechanism includes a reciprocable blockade arm and a clamp arm mounted for rotation on a common shaft. The clamp arm supports a cam follower which rides on the periphery of a cam. Heretofore, the blockade arm was connected to a contractile spring which biased the arm so that the cam follower was urged against the cam surface.
The use of a spring arrangement as described in U.S. Pat. No. 3,451,192 leads to several problems. When the blockade arm is in the "retracted" position, the spring exerts a maximal force on the arm, pressing the cam follower with excessive force against the cam. This produces rapid wear of the cam and cam follower as well as the clutch between the electric drive motor and the cam shaft. When the cam follower drops on the cam, the blockade arm moves to the "advanced" position and may bounce due to compression of the spring when the advanced position is reached, causing pronounced vibration of the blockade and adversely affecting operation of the blockade mechanism. When the blockade arm is returned to the "retracted" position, the arm moves against the force of the spring, again resulting in the cam follower being pressed with excessive force against the cam, contributing to wear of those parts and the clutch. In addition, the spring becomes stretched with use, requiring replacement or repair. Often, operating personnel attempt to "fix" the spring to restore it to its original tension by shortening the spring. This "fix" only aggravates the problem because the shorter spring may exert an even greater force on the blockade arm, worsening the wear problem. A shorter spring, moreover, is subject to failure during the operation of the machine.